PREVENTION OF EROSION BY COVERING SOIL 575 



phere and this tends to precipitate the moisture in the air, causing 

 rains. The rainfall is greater and more regular in forested area. 



Regulation of the water supply is most important if the rivers 

 are to be used for water power or navigation. Several cities on the 

 Atlantic coast, such as Savannah, Wilmington, and Philadelphia, 

 owe their importance to their position on navigable rivers supplied 

 with water largely by the Appalachian forests. Should these 

 forests be destroyed, it is possible that the frequent freshets which 



E. Block, — U. S. Forest Service 



Deep gullies on abandoned hillside land. White pine is slowly restocking this area, 

 but the erosion is still so rapid that it is difficult for the seedlings to secure a foothold. 



would follow would so fill the rivers with silt and debris that the 

 ship channels in them, already costing the government millions of 

 dollars a year to keep dredged, would become too shallow for ships. 

 If this should occur, these cities would soon lose their importance. 

 The story of how this very thing happened to the old Greek city 

 of Poseidonia is graphically told in the following lines : 



"It was such a strange, tremendous story, that of the Greek Poseidonia, 

 later the Roman Paestum. Long ago those adventuring mariners from 

 Greece had seized the fertile plain which at that time was covered with 

 forests of great oak and watered by two clear and shining rivers. They 

 drove the Italian natives back into the distant lulls, for the white man's 



